Heretofore, a so-called electronic camera (digital still camera) using CCD (Charge Coupled Device) secondary solid image pickup elements has been known. This kind of digital still camera memorizes image data of a still image, which is taken in with the CCD secondary solid image pickup elements, in a recording medium such as a memory card, a magnetic disk, and a magneto-optical disc, as photographed image data. Therefore, a film which is used in a normal camera is unnecessary.
For example, the digital still camera can output and reproduce the image of an object, which is taken in with the CCD secondary solid image pickup elements at the time of photographing, on a viewfinder. Then, a user confirms the image on the viewfinder and pushes the shutter, so that the image data, which is being taken in at this time, can be recorded in a recording medium as a photographed image.
In addition, the digital still camera can output and reproduce the image data, which has been recorded in the recording medium, on the viewfinder and also can output it to an external television monitor or a computer so as to display it like a photographed picture.
However, such a digital still camera may record image data for one frame (one image) taken in with CCD secondary solid image pickup elements, for example, in a recording medium such as a memory card, leaving its size (the number of picture elements) as it is. However, if there is a problem in the capacity of a recording medium or there is a request to increase the number of pictures to be photographed, the image size adjusting processing, such as compression of taken image data, is executed.
In addition, the digital still camera performs the image size adjusting processing on image data to be displayed, either in the case where there is a problem in the number of picture elements of the display screen or where images are magnified and displayed or are reduced and displayed on the monitor.
However, in the digital still camera, when the image size adjusting processing is performed on image data to be recorded, merely thinning out picture elements of the image data for the image size adjustment leads to a problem in that image quality becomes significantly worse owing to increase of aliasing.
In addition, in the digital still camera, it can be considered in which a high-dimensional filter is used to avoid the deterioration of image quality. However, this consideration has a problem in that the size of a hardware becomes large.